1. Field of the Invention
The invention relates to a process of chamber condition control for an etcher, and more particularly to a seasoning process for the etcher.
2. Description of the Related Art
Dielectrics material is widely used in integrated circuits; therefore, it is more often etched than other materials during the semiconductor processes. CF.sub.x plasma is often used to perform dry etching on the dielectrics material, in which etching process the high-energy electrons in the plasma bombard the CF.sub.x gas to generate various ions or atoms. The fluorine atoms or ions produced by ion bombardment react with the silicon atoms of the dielectrics material to form a volatile compound. Using the fluorine atoms in the CF.sub.x plasma and properly adjusting the ion bombardment on the thin film on the wafer and the polymer, the dielectrics material is therefore etched. However, when the amount of polymers exceeds the ion bombardment from the plasma, a polymer is formed on the wafer, which retards the etching process for the dielectrics material.
In order to enhance the conductivity of the polysilicon layer during fabrication of the semiconductor process, a titanium silicide layer 102 is often formed on a substrate 100, as shown in FIG. 1, and the substrate 100 is then covered with a silicon oxide layer 104. The silicon oxide layer 104 is then etched to form a contact window 106 or a test key 108, both of which expose the titanium silicide (TiSi.sub.x) 102. The etching process for the silicon oxide layer 104 is carried out by an inductive coupled plasma high density plasma etcher (ICP HDP etcher), so that it is necessary to balance the ion bombardment and the amounts of the polymer 110 deposition to achieve a good etching process performance. After a number of wafers undergo the foregoing process, including etching the dielectric layer 104 to expose the titanium silicide layer 102, it is found that the chamber conditions in the etcher gradually change, which causes the etching to stop. From the previous process characterizations and material analysis, the changes in the process conditions are caused by exposed TiSi.sub.x films sputtering onto an ICP source dome area, which sputtering affects the RF coupling of the inductive coupled plasma. This, in turn, results in the destruction of the balance between the ion bombardment and the amounts of the polymers 110 deposited on the wafer surface. This imbalance leads to polymer formation exceeding the ion bombardment and, as a result, the etching process for forming the contact window 106 or the test key 108 cannot be successfully performed. In addition, the change in chamber conditions also causes etching rates and etching selectivity to shift, resulting in an inability to etch the dielectric layer 104 prior to exposing the TiSi.sub.x 102. Therefore, the etching process to form the contact window 106 or the test key 108 fails.